Using chick embryo cells infected with a temperature-conditional mutant of Rous sarcoma virus, we propose to examine the earliest cell- surface changes associated with malignant transformation and with growth control. The starting point for our analysis is the increased rate of hexose transport, which is characteristic of cells transformed by RNA tumor viruses. We will investigate the relationship between this transport change and other cell-surface changes, such as alterations in cell-surface carbohydrates and membrane lipids, and changes in cellular adhesiveness and in the transport of other molecules. Cause-effect relationships between these surface alterations, the mechanisms which control their appearance, and their causal relationship to the tranformed phenotype will be analyzed.